and rodents, the boulders provide protection from the cattle and provide thermal stability at many times of the year. For Grasshopper Sparrows they are song perches for mate attraction and territorial display. They shelter the burrows for Burrowing Owls, and serve as perch sites for Greater Roadrunners and hunting posts for American Kestrels. The boulders give the West Mesa the ecological expression and the beauty provided by none other of our remaining patches of Grasslands.

Perhaps no other habitat in California has been altered as extensively since European contact as native grasslands. San Marcos Foothills has not been immune from this process. Yet, the important point is—because of its size, slopes and aspects, and associated wetlands—San Marcos Foothills supports the largest and best remaining grassland in our region. (Grasshopper Sparrows are more likely to occupy large tracts of habitat than small fragments (Vickery, 1996).)

The bird response to grasslands is complex. The SMF Grasslands are occupied extensively by birds year-round, but some breeding species are replaced by migrants that spend the fall and winter. A third group of birds, those that only pass through on migration, can be especially abundant in spring. (See Tables 2 and 3, Assemblages.)

While discussion of the Grasslands often emphasizes the species that comprise it, the structure of the grassland may play a large role in determining ecological interactions. Grasslands characterized by spaces between clusters of grasses, such as bunch grasses, apparently support the most species-rich fauna and the more complex ecological functions. In winter and spring, the dense carpet of annual grasses may be great for cattle, but it eliminates the alleys between grasses used, for example, by voles, snakes and lizards, and grassland sparrows.

Soil moisture is altered in Grasslands dominated by annuals. The rapid growth of annuals in spring sucks the moisture from the surface soils more quickly than in Grasslands dominated by perennial bunchgrasses. Oak seedlings and other herbaceous plants fare poorly in competition for moisture and sunlight; therefore oak regeneration is not as successful in exotic grassland where the grass structure tends to be more dense.

Ironically, cattle lessen the stifling effects of Grasslands dominated by annuals. By grazing preferentially on annuals, cattle bring about some openness, which in certain situations allows the germination of native annuals and the growth of perennials by mid-summer. Early ranchers introduced grass annuals from Europe because the dense and seedy growth allowed better forage for more cattle. These exotic species spread easily, especially where assisted by soil disturbance, soil compaction, or loss of competing habitats. Cattle grazed in moderate density, however, can better serve as a principal agent of control of exotic annual grasses and other exotic herbaceous growth. Removal of cattle without control of the exotic plant species will disrupt a delicate balance that in the short term protects native grasses.

More is to be learned about management and restoration on native grasslands to achieve ecological functions that occurred historically and still occur where native grasses promote an open grassland structure. In San Marcos Foothills Grasslands, the opportunities for teaching and research abound. Sufficient grassland area exists on San Marcos Foothills to allow both restoration and manipulative experimental research. [Policies Gen-1.2; Res-7.3, 7.4; Ed-6.1]

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